The present invention relates to poly(arylene ether)-polystyrene compositions, and especially relates to poly(arylene ether)-polystyrene compositions having reduced dust formation during pelletizing.
In majority of cases, thermoplastics are processed via compounding and molding operations. A compounded formulation is often isolated in the form of granulate via pelletizing. Pelletizing is the operation during which a plastic string coming out of a die of a compounding machine (e.g., an extruder) is chopped via mechanical forces into granules. These granulation forces can cause the release of small pieces of material from the surface of the string, forming dust. Dust formation is an industrial issue not only during the pelletizing step but also during transportation and further processing such as feeding to a molding machine.
U.S. Pat. No. 5,199,184 to Rosse describes a method of handling plastic granules, especially polyester granules, in which the plastic granules are first crystallized then dried in a fluidized bed such that dust particles are removed from the granules, blown upward and deposited in a cyclone.
U.S. Pat. No. 5,296,563 to Gottschalk et al. describes a process of preparing thermoplastic molding materials whereby the poly(phenylene ether) component, initially present in pulverulent form, is subjected to compacting or sintering under pressure to decrease the proportion of free fine material.
The methods known in the art require special equipment achieve dust reduction. There continues to be a need for thermoplastic compositions that are inherently less susceptible to dust formation.
Reduced dust formation is exhibited by a thermoplastic composition comprising: (a) about 20 to about 80 weight percent of a poly(arylene ether); (b) about 5 to about 80 weight percent of a polystyrene; (c) optionally, about 0.1 to about 15 weight percent of a rubber material; and (d) about 0.1 to about 5 weight percent of a metal hydroxide compound capable of releasing water during a compounding or molding step; wherein all weight percents are based on the weight of the entire composition.
A thermoplastic composition exhibiting reduced dust formation comprises: (a) about 20 to about 80 weight percent of a poly(arylene ether); (b) about 5 to about 80 weight percent of a polystyrene; (c) about 0.1 to about 15 weight percent of a rubber material; and (d) about 0.1 to about 5 weight percent of a metal hydroxide compound capable of releasing water during a compounding or molding step; wherein all weight percents are based on the weight of the entire composition.
The composition comprises at least one poly(arylene ether) resin. Although all conventional poly(arylene ether)s can be employed with the present invention, polyphenylene ethers (xe2x80x9cPPExe2x80x9d) are preferred. Poly(arylene ether)s per se, are known polymers comprising a plurality of structural units of the formula: 
wherein for each structural unit, each Q1 is independently halogen, primary or secondary lower alkyl (that is, alkyl containing from one to about seven carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each Q2 is independently hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for Q1. Preferably, each Q1 is alkyl or phenyl, especially C1-4 alkyl, and each Q2 is hydrogen.
Both homopolymer and copolymer poly(arylene ether)s are included. The preferred homopolymers are those containing 2,6-dimethylphenylene ether units. Suitable copolymers include random copolymers containing, for example, such units in combination with 2,3,6-trimethyl-1,4-phenylene ether units or copolymers derived from copolymerization of 2,6-dimethylphenol with 2,3,6-trimethylphenol. Also included are poly(arylene ether)s containing moieties prepared by grafting vinyl monomers or polymers such as polystyrenes, as well as coupled poly(arylene ether)s in which coupling agents such as low molecular weight polycarbonates, quinones, heterocycles and formals undergo reaction in known manner with the hydroxy groups of two poly(arylene ether) chains to produce a higher molecular weight polymer. Poly(arylene ether)s of the present invention further include combinations of any of the above.
The poly(arylene ether)s generally have a number average molecular weight of about 3,000 to about 40,000 and a weight average molecular weight of about 20,000 to about 80,000, as determined by gel permeation chromatography. The poly(arylene ether) generally has an intrinsic viscosity of about 0.10 to about 0.60 deciliters per gram (dL/g), preferably about 0.29 to about 0.48 dL/g, all as measured in chloroform at 25xc2x0 C. It is also possible to utilize a high intrinsic viscosity poly(arylene ether) and a low intrinsic viscosity poly(arylene ether) in combination. Determining an exact ratio, when two intrinsic viscosities are used, will depend somewhat on the exact intrinsic viscosities of the poly(arylene ether) used and the ultimate physical properties that are desired.
The poly(arylene ether) is typically prepared by the oxidative coupling of at least one monohydroxyaromatic compound such as 2,6-xylenol or 2,3,6-trimethylphenol. Catalyst systems are generally employed for such coupling; they typically contain at least one heavy metal compound such as a copper, manganese or cobalt compound, usually in combination with various other materials.
Particularly useful poly(arylene ether)s for many purposes are those which comprise molecules having at least one aminoalkyl-containing end group. The aminoalkyl radical is typically located in an ortho position to the hydroxy group. Products containing such end groups may be obtained by incorporating an appropriate primary or secondary monoamine such as di-n-butylamine or dimethylamine as one of the constituents of the oxidative coupling reaction mixture. Also frequently present are 4-hydroxybiphenyl end groups, typically obtained from reaction mixtures in which a by-product diphenoquinone is present, especially in a copper-halide-secondary or tertiary amine system. A substantial proportion of the polymer molecules, typically constituting as much as about 90 weight percent of the polymer, may contain at least one of said aminoalkyl-containing and 4-hydroxybiphenyl end groups.
It will be apparent to those skilled in the art from the foregoing that the poly(arylene ether)s include all those presently known, irrespective of variations in structural units or ancillary chemical features.
A suitable amount of poly(arylene ether) in the composition is about 20 to about 80 weight percent, with a preferred amount being about 20 to about 70 weight percent. An amount of about 30 to about 60 weight percent is more preferred.
The composition further comprises at least one polystyrene. The term xe2x80x9cpolystyrenexe2x80x9d as used herein includes polymers prepared by methods known in the art including bulk, suspension and emulsion polymerization, which contain at least 25 weight percent of structural units derived from a monomer of the formula: 
wherein R1 is hydrogen, lower alkyl or halogen; Z1 is vinyl, halogen or lower alkyl; and p is from 0 to 5. These resins include homopolymers of styrene, chlorostyrene and vinyltoluene; random copolymers of styrene with one or more monomers illustrated by acrylonitrile, butadiene, alpha-methylstyrene, ethylvinylbenzene, divinylbenzene and maleic anhydride; and rubber-modified polystyrenes comprising blends and grafts, wherein the rubber is a polybutadiene or a rubbery copolymer of about 70 to about 98 weight percent styrene and about 2 to about 30 weight percent diene monomer. Polystyrenes are known to be miscible with poly(arylene ether)s in all proportions, and the composition may contain polystyrene in an amount of about 20 to about 80 weight percent and more often about 20 to about 70 weight percent, based on the weight of the entire composition. A polystyrene amount of about 30 to about 60 weight percent is preferred.
The composition optionally further comprises at least one rubber material. Suitable rubber materials include those comprising a styrenic block copolymer. Styrenic block copolymers suitable for the polymer compositions according to the invention comprise blocks built up from a vinyl aromatic compound, for example, styrene, and blocks built up from an olefinic compound, for example butadiene, ethylene and/or propylene. Suitable are linear block copolymers, radial teleblock copolymers and so-called xe2x80x9ctaperedxe2x80x9d block copolymers, i.e. block copolymers built up from blocks which are bonded together via a xe2x80x9crandomxe2x80x9d copolymer of the vinyl aromatic compound and (hydrogenated) diene compound. The styrenic block copolymers may be unsaturated, i.e., they may contain residual olefinic unsaturation. Alternatively, the styrenic block copolymers may be saturated, i.e., they may be essentially free of olefinic unsaturation.
Suitable unsaturated styrenic block copolymers may have number average molecular weights of about 50,000 to about 200,000, with molecular weights of about 80,000 to about 150,000 being preferred, and molecular weights of about 100,000 to about 130,000 being more preferred. The unsaturated styrenic block copolymer may be present in an amount of about 0.1 to about 10 weight percent, preferably about 0.3 to about 5 weight percent, more preferably about 0.5 to about 2 weight percent, based on the weight of the entire composition. Suitable saturated styrenic block copolymers may have number average molecular weights of about 50,000 to about 500,000, with molecular weights of about 100,000 to about 400,000 being preferred and molecular weights of about 200,000 to about 300,000 being more preferred. The optional styrenic block copolymers may be present in an amount of about 1 to about 15 weight percent, preferably about 3 to about 10 weight percent, more preferably about 5 to about 8 weight percent, based on the weight of the entire composition.
Suitable styrenic block copolymers are commercially available from a number of sources, including Phillips Petroleum under the trademark SOLPRENE(copyright), Shell Chemical Company under the trademark KRATON(copyright), and Kuraray under the trademark SEPTON(copyright). Suitable materials include the unsaturated styrenic block copolymers in the KRATON(copyright) D series (styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS)), and the saturated styrenic block copolymers in the KRATON(copyright) G series (styrene-ethylene/butylene-styrene (SEBS) and styrene-ethylene/propylene-styrene (SEPS)). Especially preferred are the materials sold as KRATON(copyright) G 1650 and 1651.
In addition to the poly(arylene ether), the polystyrene, and the optional rubber material, the composition further comprises a metal hydroxide compound capable of releasing water during the compounding and or molding step. Suitable metal hydroxide compounds include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, their respective hydrates, and the like. Aluminum hydroxide and its hydrates are preferred. Metal hydroxide compounds are commercially available. For example, suitable aluminum hydroxides may be obtained from Alcoa Corporation under the grade names C333, M2B and M15B. The metal hydroxide may be employed in an amount effective to reduce dust formation during granulation of the resin composition and/or handling of the resultant granules. The amount of metal hydroxide is generally in the range of about 0.1 to about 5 weight percent, preferably about 0.5 to about 2 weight percent, more preferably about 0.75 to about 1.5 weight percent, based on the weight of the entire composition.
The composition may optionally comprise one or more mineral oils to improve the low temperature impact strength of the composition. Useful mineral oils are of the type known as white mineral oils. They are a complex mixture of saturated paraffinic and naphthenic hydrocarbons and are preferably free of aromatic compounds, sulfur-containing compounds, acids, and other impurities. White mineral oils are available in a wide range of viscosities, and the useful oils have Saybolt viscosities ranging from about 50 to about 350 centipoise at 100xc2x0 F. Examples of suitable oils are the white mineral oils sold under the trademarks PROTOL(copyright), GLORIA(copyright), and KAYDOL(copyright) by Witco Chemical Company, and the mineral oils sold under the trademark FLEXON(copyright) by Esso Nederland BV. A particularly preferred mineral oil is FLEXON(copyright) 834. A more detailed description of useful mineral oils can be found in U.S. Pat. No. 2,619,478.
One or more mineral oils may be employed in the composition at from 0 to about 5 weight percent, preferably about 0.1 to about 2.5 weight percent, more preferably about 0.25 to about 1 weight percent.
The composition preferably contains one or more antioxidants. Suitable antioxidants include organophosphites, for example, tris(nonyl-phenyl)phosphite, tris(2,4-di-tert.-butylphenyl)phosphite, bis(2,4-di-tert.-butylphenyl)pentaerythritol diphosphite or distearyl pentaerythritol diphosphite; hindered phenols, such as alkylated monophenols, polyphenols and alkylated reaction products of polyphenols with dienes, such as, for example, tetrakis[methylene(3,5-di-tert.-butyl-4-hydroxyhydrocinnamate)] methane, 3,5-di-tert.-butyl-4-hydroxyhydrocinnamate octadecyl, butylated reaction products of para-cresol and dicyclopentadiene, alkylated hydroquinones, hydroxylated thiodiphenyl ethers, alkylidene-bisphenols, O-, N- and S-benzyl compounds, such as, for example, 3,5,3xe2x80x2,5xe2x80x2-tetra-tert.-butyl-4,4xe2x80x2-dihydroxydibenzyl ether, octadecyl 4-hydroxy-3,5-dimethylbenzyl-mercaptoacetate, tris-(3,5-di-tert.-butyl-4-hydroxybenzyl)-amine and bis-(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl) dithioterephthalate, esters of beta-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid with monohydric or polyhydric alcohols, esters of beta-(5-tert.-butyl-4-hydroxy-3-methylphenyl)-propionic acid with monohydric or polyhydric alcohols, amides of beta-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid, and hindered phenol-substituted triazine triones such as 1,3,5-tris(3,5-di-tert.-butyl-4-hydroxybenzyl)-s-triazinetrione; and esters of thioalkyl or thioaryl compounds, such as, for example, distearylthiopropionate, dilaurylthiopropionate, ditridecylthiodipropionate. Preferred antioxidants include organophosphites and hindered phenols. Highly preferred antioxidants include tetrakis[methylene(3,5-di-tert.-butyl-4-hydroxyhydrocinnamate)] methane sold by Ciba Specialty Chemicals under the trademark IRGANOX(copyright) as IRGANOX(copyright) 1010, and 1,3,5-tris(3,5-di-tert.-butyl-4-hydroxybenzyl)-s-triazinetrione sold by Ciba Specialty Chemicals under the trademark IRGANOX(copyright) as IRGANOX(copyright) 3114, as well as antioxidant combinations comprising at least one of these.
The antioxidant, when employed, may be present in an amount of about 0.1 to about 3 weight percent, preferably about 0.25 to about 2.5 weight percent, more preferably about 0.5 to about 2 weight percent, based on the weight of the entire composition.
Various additives may be used in the formulation such as flame retardants, stabilizers, pigments, reinforcing agents, processing aids, plasticizers, and the like.
Different inorganic additives may be used in poly(arylene ether) resins as reinforcing agents, heat stabilizers, colorants (organic and inorganic pigments, dyes) and electroconductive additives. Some representative examples cover the compounds such as various types of silicas and aluminas, zeolites, titanium dioxide, potassium titanate and titanate whiskers, calcium carbonate, calcium sulfates, kaolin, talc, wollastonite, limestone products, mica, barium sulfate, carbon blacks, glass beads and fibers, etc. Especially preferred additives are the filamentous and chopped glass fibers. Such glass fibers may be untreated or, optionally, treated with a silane or titanate coupling agent, and are well known in the art and widely available from a number of manufacturers. Such additives can be used in amounts of about 0.1 to about 50 weight percent, preferably about 0.5 to about 30 weight percent and more preferably about 1 to about 20 weight percent.
Many stabilizers used in plastics can be part of a poly(arylene ether) formulation, e.g. UV stabilizers, radical and hydroperoxide scavengers such as hindered phenols, hindered amines, benzofuranones, benzotriazoles, benzophenones, hydroxylamines, organic phosphites and phosphates, thioethers, thioesters, zinc oxide, zinc sulfide, and the like.
Other additives which can be used in the composition include: lubricants to enhance mold release and flow such as metallic stearates, hydrocarbons (including polyolefines and Teflon), fatty acids and fatty alcohols; exothermic and/or endothermic blowing agents; halogen based, metal hydrate based or phosphorous based flame retardants; plasticizers which increase flexibility, workability and distensibility such as glutarates, adipates, azelates, sebacates, phthalates, etc.; and adhesion promoters (epoxies, phenolics, acrylates, terpenes, etc).
The composition can be prepared by combining the poly(arylene ether), the polystyrene, the rubber compound, and the metal hydroxide compound, as well as any optional ingredients, using any of the known compounding equipment and procedures. For example, a dry pre-blend of all ingredients can be formed; the pre-blend can be heated to a temperature sufficient to cause melting (e.g., at about 250xc2x0 C. to 350xc2x0 C.); and the melted pre-blend can be extruded in a single or twin screw extruder. The extruded material can be chopped, cut or ground to smaller size and injection molded (e.g., about 250xc2x0 C. to 320xc2x0 C.) to desired shape and size. Alternatively, the various components can be blended at different times during the extrusion process. Steam stripping and vacuum venting may advantageously be used during the compounding and/or extruding steps to remove the generated volatiles.
All cited patents are incorporated herein by reference.